Pyrocumulonimbus Black Carbon Morphology and Mixing State Control Direct Radiative Effect

PAYTON BEELER, Joshin Kumar, Joshua P. Schwarz, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 558
     Working Group: Carbonaceous Aerosol

Abstract
Atmospheric black carbon (BC) aerosol is an important component of Earth’s climate system in part because of its ability to absorb incoming solar radiation. Among the largest sources of atmospheric BC are wildfires and other types of biomass burning. High-energy wildfires can produce pyrocumulonimbus events (pyroCbs) that inject smoke into the upper troposphere and lower stratosphere (UTLS), where it can remain suspended for several months. Because of BC’s ability to absorb incoming sunlight, it is predicted to have a net positive direct radiative effect (DRE) and be an atmospheric warming agent. However, the location of BC in the atmosphere and its mixing state with non-BC materials have significant impacts on the DRE of BC. PyroCb BC particles in particular are unique because of their mixing state with other non-BC materials, which manifest as thick coatings on the surface of BC. Previous studies have produced conflicting estimates of the DRE of BC from a pyroCb event, which may be due in part to differing representations of BC morphology and mixing state in radiative transfer models. This study utilizes particle-resolved measurements from within a pyroCb plume and particle-resolved simulations to benchmark the effectiveness of different BC model parameterizations in calculating the DRE of pyroCb BC. We find that the DRE of pyroCb BC is highly dependent on the choice of BC representation when calculating BC optical properties, and that detailed representation of BC mixing state is required for more accurate estimation of BC DRE.